Autism is a disorder that is defined behaviorally, for which no dominant etiology or neurobiological marker has yet been identified. Research has been constrained by the need for reliable and standard diagnostic formulations of autism to ensure comparability of populations. The diagnosis of autism is made complicated by a number of factors. Autism occurs across a range of intellectual levels from severe mental retardation to above average intelligence. Autism is a spectrum disorder. Genetic studies indicate that what is transmitted may be a familial risk for communication, social, and perhaps personality disorders. In addition, because the primary features of autism involved social and communicative deficits, the contexts in which these behaviors are observed are very important. What the examiner does with the child or adult affects the subject's behavior and the examiner's judgments. Assessments standardized both in what aspect of the subject's behavior is scored and what the examiner does (or asks an informant about) are much needed. There is clearly a trade-off between standardized approaches and the need for clinical flexibility in dealing with a population that may range from one extreme to the other in IQ and age. A week-long training workshop provides hands-on training to researchers in the use of two instruments for the diagnosis of autism: The Autism Diagnostic Interview-Revised (ADI-R; Lord, Rutter & Le Couteur, 1994), a semi-structured investigator-based parent interview, and the Autism Diagnostic Observation Schedule-Generic (ADOS-G), a recently reorganized combination of the ADOS (Lord, Rutter, Good, Mawhood, Heemsbergen & Jordan, 1989), an observational protocol for social and communicative behavior, and the Pre-Linguistic Autism Diagnostic Observation Schedule (PL-ADOS: DiLavore, Lord & Rutter, 1995), an observational protocol comparable to the ADOS but designed for use with young, non-verbal children. The goal of the workshop is for participants to attain familiarity with the instruments and to provide a general knowledge of issues in research diagnoses of autism spectrum disorders.